Fluid machines are conventionally known in which an expansion mechanism, an electric motor and a compression mechanism are connected by a single rotary shaft. In such a fluid machine, the expansion mechanism generates power by expanding fluid introduced thereinto. The power generated by the expansion mechanism, together with power generated by the electric motor, is transmitted to the compression mechanism by the rotary shaft. Then, the compression mechanism is driven by the power transmitted from the expansion mechanism and the electric motor to suck the fluid and compress it.
In such a fluid machine, the expansion mechanism is heated by high-temperature fluid discharged from the compressor. Thus, when used for hot water supply, the fluid machine causes a decrease in the discharge gas temperature of the compressor, which decreases the hot water supply temperature. On the other hand, when used for air conditioning, the fluid machine causes a decrease in supply air temperature during heating operation and degrades the performance during cooling operation. Furthermore, the expansion mechanism itself causes an internal heat loss, whereby its power recovery effect is set off.
To prevent these problems of performance degradation and decrease in power recovery effect, Published Japanese Patent Application No. 2005-106064, for example, discloses a technique in which a heat insulator is attached to the expansion mechanism.